An aneurysm is an abnormal ballooning or dilation of a blood vessel. A cerebral aneurysm is an aneurysm in an artery or vein in the brain. Cerebral aneurysms are more common in adults than in children and more common in women than in men. Cerebral aneurysms commonly arise at the bifurcations of major arteries; most cerebral aneurysms arise on the circle of Willis (where several arteries join near the bottom of the brain) or the middle cerebral artery (MCA) bifurcation.
A common complication of a cerebral aneurysm is rupture, which results in profuse bleeding and causes serious complications including hemorrhagic stroke, permanent nerve damage, hydrocephalus, vasospasm, and/or death. Another complication of a cerebral aneurysm is stroke. Blood pools in the aneurysm, where it becomes isolated from the flow of blood in the brain and subsequently clots. Clots of various sizes can then break off, escape from the cerebral aneurysm into the cerebral vasculature and lodge downstream, causing a stroke.
A variety of options exist for treating cerebral aneurysms. As one example, the aneurysm is clipped from outside before or after it bursts to isolate the aneurysm from the vasculature. However, such clipping requires highly invasive surgical intervention in the brain through the skull. Further, clipping the aneurysm after it bursts does nothing to prevent the potentially-fatal consequences of rupture. It is preferable to treat the aneurysm before it bursts, because patients who receive treatment for an unruptured aneurysm generally require less therapy and recover more quickly. As an example of such treatment, the aneurysm is filled with wire coils. Conventional catheterization techniques are used to insert a catheter into the patient's vasculature at a location outside the brain, such as the groin or the neck, and advance the catheter to the aneurysm using angiography, after which the coils are delivered through the catheter to the aneurysm. The coils fill the aneurysm before it bursts, block it from circulation, and cause the blood to clot. However, the coils may become dislodged from the aneurysm and enter the vasculature, causing stroke in the same manner as blood clots that become dislodged from the aneurysm. Further, smaller clots may still break off and escape from the cerebral aneurysm, resulting in stroke.